Optical temperature sensing is crucial to many applications, especially where other methods of temperature sensing are unsuited, such as those involving high electric or magnetic fields, etc. Optical temperature sensing includes a number of techniques, such as pyrometry and luminescence techniques. However, conventional systems suffer from a lack of sensitivity across the full scale range, either having a low sensitivity at lower temperatures or a drop off in usable range at higher temperatures. Conventional systems utilize a filtered select short wavelength light to excite the thermal responsive coating, limiting the choices of light sources to excite the coating, and causing the systems to be sensitive to noise from background lighting.
The current state of the art uses luminescent dyes or phosphors to measure global surface temperature, a technique commonly referred to as the Temperature-Sensitive Paint (TSP) technique. Short wavelength light sources—either UV, violet (˜400 nm) or blue (˜460 nm)—are used to excite the luminescent material. The emitted light shifts to longer wavelengths which can be detected using a spectral filter that eliminates the excitation light from the detector. Additionally, temperature indicating paints capture peak temperature achieved through an irreversible color change after several minutes at that condition. These color changes are predetermined thermal bands that register the peak temperature if the peak temperature falls within the band.
The disadvantages of these luminescent sensors are the use of the filtered excitation light and the high cost and complexity of the detection systems. Generating high intensity stable short wavelength light for excitation is costly and limited to dark areas where background light becomes a potential error source or where the luminescent signal intensity must overcome the background. However, high intensity short wavelength excitation light tends to cause degrading of the emitted light over time.